首先明白 动态代理和静态代理的区别；
静态代理：①持有被代理类的引用 ② 代理类一开始就被加载到内存中了（非常重要）
动态代理：JDK中的动态代理中的代理类是动态生成的。并且生成的动态代理类为$Proxy0
静态代理实例1、创建一个接口：
package proxy;
public interface People {
public void zhaoduixiang()throws Throwable;
}
2、创建一个实现类，张三，张三能够吃饭，张三可以找对象
package proxy;
public class ZhangSan implements People {
public void zhaoduixiang() throws Throwable{
System.out.println(" 我只要漂亮的");
}
}
3、创建一个实现父类，父类持有张三的引用
package proxy;
public class HisDady implements People {
ZhangSan zs;
public HisDady(ZhangSan zs){
this.zs=zs
}
public void zhaoduixiang() throws Throwable{
before()
zs.zhaoduixiang();
afger()
}
public void afger() throws Throwable{
System.out.println(" 家境要好");
}
public void before() throws Throwable{
System.out.println(" 要有学历");
}
}
动态代理:
1、创建一个申明类ProxyHandler
package proxy; import java.awt.event.InvocationEvent;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method; public class ProxyHandler implements InvocationHandler{
People peaple=null;
public ProxyHandler(People people){
this.peaple=people;
} public void before()throws Throwable{
System.out.println("吃饭之前要洗手");
}
public void after()throws Throwable{
System.out.println("吃饭以后要洗碗");
} @Override
public Object invoke(Object proxy, Method method, Object[] args)
throws Throwable {
before();
method.invoke(peaple,null);
after();
return null;
} }
2、创建一个test类 。
package proxy; import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.lang.reflect.Proxy; import sun.misc.ProxyGenerator; public class Test {
public static void main(String[] args) throws Throwable{
System.out.println("JDK写的动态代理"); People people=(People) Proxy.newProxyInstance(People.class.getClassLoader(),
new Class[]{People.class}, new ProxyHandler(new ZhangSan()));
people.eat();
}
public void sleep() throws Throwable{
System.out.println("睡觉");
}
public void sport()throws Throwable{
System.out.println("睡觉");
}
}
执行结果：
打印如图所示，那么People一定执行了ProxyHandler 中的invoke方法，并且首先执行before() 再执行method.invoke(peaple,null);最后执行 after();
那么问题来了，为什么会这么执行了？我们明明调用的People.eat()方法啊。
解析步骤：我们打印此时的People对象的名字，看看接口对应中到底是个什么东西：
在test中的 people.eat();后面加入：
System.out.println(people.getClass().getName());
打印结果为：Proxy.$Proxy0 ,这是个什么鬼东西，原来，people对象中保存的是一个类名为 $Proxy0的对象，我们调用的是$Proxy0的eat()方法，
所以我们最好看看$Proxy0的源码:
如何读取$Proxy0的代码（由于$Proxy0JDK会自动删除，所以我们要把它写入到一个对应的文件中 ，代码如下）：
package proxy; import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.lang.reflect.Proxy; import sun.misc.ProxyGenerator; public class Test {
public static void main(String[] args) throws Throwable{
System.out.println("JDK写的动态代理"); People people=(People) Proxy.newProxyInstance(People.class.getClassLoader(),
new Class[]{People.class}, new ProxyHandler(new ZhangSan()));
people.eat(); System.out.println(people.getClass().getName());
creatProxyClassFile();
}
public static void creatProxyClassFile(){
byte[] data=ProxyGenerator.generateProxyClass("$Proxy0", new Class[]{People.class});
try {
FileOutputStream out= new FileOutputStream("$Proxy0.class");
out.write(data);
out.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} }
public void sleep() throws Throwable{
System.out.println("睡觉");
}
public void sport()throws Throwable{
System.out.println("睡觉");
}
}
打开对应的项目工作空间，你会发现一个对应$Proxy0文件；
那么其中有什么玄妙，导致我们调用$Proxy0.eat()方法的时候，会调用invoke()方法了
我们看看Proxy0类的源码，请用反编译软件打开Proxy0.class：
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.lang.reflect.UndeclaredThrowableException;
import proxy.People; public final class $Proxy0 extends Proxy
implements People
{
private static Method m1;
private static Method m3;
private static Method m0;
private static Method m2; public $Proxy0(InvocationHandler paramInvocationHandler)
throws
{
super(paramInvocationHandler);
} public final boolean equals(Object paramObject)
throws
{
try
{
return ((Boolean)this.h.invoke(this, m1, new Object[] { paramObject })).booleanValue();
}
catch (Error|RuntimeException localError)
{
throw localError;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
} public final void eat()
throws Throwable
{
this.h.invoke(this, m3, null);
} public final int hashCode()
throws
{
try
{
return ((Integer)this.h.invoke(this, m0, null)).intValue();
}
catch (Error|RuntimeException localError)
{
throw localError;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
} public final String toString()
throws
{
try
{
return (String)this.h.invoke(this, m2, null);
}
catch (Error|RuntimeException localError)
{
throw localError;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
} static
{
try
{
m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[] { Class.forName("java.lang.Object") });
m3 = Class.forName("proxy.People").getMethod("eat", new Class[0]);
m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);
m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
return;
}
catch (NoSuchMethodException localNoSuchMethodException)
{
throw new NoSuchMethodError(localNoSuchMethodException.getMessage());
}
catch (ClassNotFoundException localClassNotFoundException)
{
throw new NoClassDefFoundError(localClassNotFoundException.getMessage());
}
}
}
请注意其中的一些方法和属性，比如public final void eat() throws Throwable { this.h.invoke(this, m3, null); } ，其中 该对象的eat()方法是调用的invoke 方法，那h是什么意思，
因为Proxy0 ：public final class $Proxy0 extends Proxy，在Proxy中查看 发现： protected InvocationHandler h;,所以h就是一个我们传入的InvocationHandler 对象，也就是调用的是InvocationHandler 的invoke方法。 这样我们就明白了为什么会出现console中打印的结果了吧。
纯手写动态代理，不使用任何JDK：
1、 创建一个MyInvocationHandler 接口，模拟InvocationHandler
package proxy;
import java.lang.reflect.Method;
public interface MyInvocationHandler {
public Object invoke(Object proxy,Method method,Object args)
throws Throwable;
}
2、实现该接口MyProxyHandler，模拟ProxyHandler，和原来动态代理完全一个样，只是改了下代码形式
package proxy;
import java.lang.reflect.Method;
public class MyProxyHandler implements MyInvocationHandler {
People peaple=null;
public MyProxyHandler(People people){
this.peaple=people;
}
public Object invoke(Object proxy, Method method, Object args)
throws Throwable {
before();
method.invoke(peaple,null);
after();
return null;
}
public void before(){
System.out.println("吃饭之前要洗手");
}
public void after(){
System.out.println("吃饭以后要洗碗");
}
}
3、新建一个Proxy类，MyProxy，用来模拟Proxy
package proxy; import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method; import javax.tools.JavaCompiler;
import javax.tools.JavaCompiler.CompilationTask;
import javax.tools.StandardJavaFileManager;
import javax.tools.ToolProvider; import org.omg.CORBA.INTF_REPOS; public class MyProxy {
static String rt="\r\t";
public static Object createProxyInstance(ClassLoader loader,Class intf,MyInvocationHandler handler){
try {
Method[] methods=intf.getMethods();
//1用流的方式创建一个Java文件，
String proxyClass="package proxy;"+rt
+"import java.lang.reflect.Method;"+rt
+"public class $Proxy0 implements "+intf.getName()+"{"+rt
+"MyInvocationHandler h;"+rt
+"public $Proxy0(MyInvocationHandler h)"+"{"+rt
+"this.h= h;"+rt+"}"
+getMethodString(methods,intf)+rt+"}";
//2 把类生成文件，
String filename="D:/WorkSpace/proxy/src/proxy/$Proxy0.java";
File f=new File(filename); FileWriter fw=new FileWriter(f);
fw.write(proxyClass);
fw.flush();
fw.close(); //3编译Java文件
JavaCompiler compiler=ToolProvider.getSystemJavaCompiler();
StandardJavaFileManager fileMgr =compiler.getStandardFileManager(null, null, null);
Iterable units=fileMgr.getJavaFileObjects(filename);
CompilationTask t=compiler.getTask(null, fileMgr, null, null, null, units);
t.call();
fileMgr.close(); //把class加载到内存中去
MyClassLoader loader1=new MyClassLoader("D:/WorkSpace/proxy/src/proxy/");
Class proxy0Class=loader1.findClass("$Proxy0");
Constructor m=proxy0Class.getConstructor(MyInvocationHandler.class);
Object o=m.newInstance(handler);
return o;
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (NoSuchMethodException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (SecurityException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (InstantiationException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IllegalAccessException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IllegalArgumentException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (InvocationTargetException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return null; }
public static String getMethodString(Method[] methods,Class intf){
String proxyMe="";
for(Method method: methods){
proxyMe+="public void "+method.getName()+"() throws Throwable {"+rt
+"Method md= "+intf.getName()+".class.getMethod(\""+method.getName()
+"\",new Class[]{});"+rt
+"this.h.invoke(this,md,null);"+rt+"}"+rt; }
return proxyMe;
}
}
4、创建一个测试：
package proxy; import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.lang.reflect.Proxy; import sun.misc.ProxyGenerator; public class Test {
public static void main(String[] args) throws Throwable{
System.out.println("JDK写的动态代理"); People people=(People) Proxy.newProxyInstance(People.class.getClassLoader(),
new Class[]{People.class}, new ProxyHandler(new ZhangSan()));
people.eat(); /* People people1=(People) MyProxy.createProxyInstance(People.class
.getClassLoader(),People.class, new MyProxyHandler(
new ZhangSan()));
System.out.println(people1.getClass().getName());
System.out.println("自己写的动态代理");
people1.eat(); */ System.out.println(people.getClass().getName());
creatProxyClassFile();
}
public static void creatProxyClassFile(){
byte[] data=ProxyGenerator.generateProxyClass("$Proxy0", new Class[]{People.class});
try {
FileOutputStream out= new FileOutputStream("$Proxy0.class");
out.write(data);
out.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} }
}
结果：
此次是我观看动脑学院免费教学课后的练习，非常感谢Jack老师，老师讲的很好，我学了很多。